1. Field of the Invention
The present invention pertains to the art of security screening systems and, more particularly, to an interactive security screening system that focuses a sample processing system on particular portions of a collected sample and employs one or more processes to screen the collected sample for threat residue.
2. Discussion of the Prior Art
Since Sep. 11, 2001, protection against terrorist threats has become a national priority. This priority extends from the protection of government facilities inside the U.S. and abroad to the protection of private businesses and venues. Various types of threats have been postulated, including attacks using explosive, chemical and biological agents, as well as nuclear and radiological (dirty) bombs. The diversity of this threat has created complex security challenges for national, state, and local governments, the transportation industry, private businesses, and even individuals. Total expenditures related to Homeland Security topped $100B in one year and billions more have been allocated in Federal, Supplemental Appropriations, and State/Local spending. Increasingly, U.S. businesses are devoting more revenue to security systems, with expenditures reaching tens of billions. Growth in the homeland security industry is expected to be vigorous over the next decade. Motivated by the wide diversity of potential threats and by the inadequacy of currently available systems, government investments in research and development are strong.
Of the various threats postulated, explosives remain the number one choice of terrorists. Indeed, many experts and reports have noted that, in the case of terrorist activity, the statistical evidence is compelling, the primary threat is bombs. At present, two types of detection systems are in use to combat this threat, i.e., bulk detection systems and trace detection systems. Bulk detection systems identify the presence of a large or threat quantity of explosives. In contrast, trace detection systems identify the presence of residual contamination associated with explosives. That is, trace detection identifies whether an object or person has come into contact with or handled explosives.
Bulk systems can cost more than $1M per portal, while trace detection system generally run in the order of tens of thousands of dollars. Often times, installation and annual maintenance costs will exceed the original price of the system. In the case of trace explosive detection, currently deployed systems were developed primarily for the use of analytical chemists in laboratories and only later adapted for field use. Unfortunately, these systems suffer from long clearance times following a positive detection (15-30 minutes), have exceedingly high false alarm rates and require extensive training to ensure proper use and maintenance. Given the high price associated with the use of bulk detection systems and their lack of suitability for many screening tasks, such as the screening of people, trace detection systems are used with increased frequency and are most often selected for applications outside of aviation security.
The use of trace explosive detection systems is based on widely accepted scientific evidence indicating that handling or otherwise contacting explosives leaves trace residue on hands, clothes, and other materials or surfaces. The trace residue is of a high concentration and is difficult to eradicate. The entire justification for the Federal Aviation Administration's trace explosive detection program is based on this fact. Indeed, contamination is expected to be so extensive and difficult to eliminate that currently installed aviation trace explosive detection systems depend on secondary contamination, i.e., contamination transferred from an individual's hands and clothes to their baggage. Thus, the baggage is sampled for trace explosives and subjected to detection systems for analysis. While currently deployed trace detection systems have high sensitivity, the systems suffer from high operational burdens, poor sampling efficiencies, high false alarm rates and low throughput.
It is known that explosive contamination can vary widely over small spatial distances. Studies have shown that trace residue levels can differ by 10,000 fold over distances as small as a few centimeters. Unfortunately, currently available trace explosive detection systems sample only from limited spatial areas, retain no sample spatial information and recover samples from only a small section of the sample acquisition surface. By sampling from only a small area, often times trace residue is not detected even when present at detectable levels elsewhere on the sample acquisition surface. In addition, currently available sample acquisition methods are not optimized to collect particulates in the size and size range distribution most pertinent for explosives detection. In particular, most conventional trace detection systems, such as ion mobility spectrometers, require that the sample acquisition surface be clear of substances that could interfere with the measurement. Unfortunately, many substances that would improve the efficiency of sample recovery, such as adhesives, are not compatible with conventional systems and therefore cannot be utilized.
The need for a pristine sample acquisition surface or medium has resulted in two primary sample acquisition methods employed in existing trace detection systems such as swabbing (or swiping) an object and air jets that dislodge and test residue from an object. However, both of these methods are limited in sample recovery efficiency and, as stated above, fail to retain any of the spatial information of the sample or surface. Simple swabbing (or swiping) methods tend to leave large particles on the surface, typically recovering only smaller particles. Other methods, such as the above described air jet systems, often times dislodge larger particles, but leave smaller particles on the surface. Simply put, both of these techniques fail to recover a significant fraction of the existing trace contamination.
In addition to the above described shortcomings, problems exist with sample reproducibility when using swabbing techniques. Extensive operator training is required to achieve even moderately reproducible results. The required operator training not only significantly increases operational costs, but the intensity of operator involvement required to obtain a good and consistent sample significantly reduces throughput rates. In any case, additional information, particularly more detailed information regarding a likely spatial distribution of trace sample collection, would not only improve the probability of detection but, by eliminating areas that are not relevant and by permitting image analysis as a secondary level of processing, also improve the signal-to-noise ratio. Currently available systems do not permit such resolution.
Finally, existing systems do not to provide feedback to the operator or subject as to the reliability of contact or the force applied during contact (which can impact collection efficiency) and, as such, often fail to achieve adequate sample recovery. In addition to preserving some spatial information about the sample, there is also a need to determine where, on the sampling surface, the trace contamination is most likely to be present. In conventional swabbing systems and in novel systems that enable wider area analysis, such information would improve the signal-to-noise ratio of the analysis by focusing the detection and analysis on the area with the highest likelihood of contamination and by eliminating background signals that can cause unnecessary false alarms.
Therefore, despite the existence in the art of security screening systems, there still exists a need for an improved security screening system. More specifically, there exists a need for an interactive security screening system that provides feedback to test subjects and focuses detection on portions of a sample that are most likely to contain trace or threat residue.